Stream Erosion and Transportation
Running water is all precipitation (rain, snow, etc) that falls on Earth that is pulled downhill by gravity. This running water originally gets its energy from the sun, since that is the source of energy for evaporation (which must occur for precipitation to form).
Running water breaks up the rocks by a mechanical weathering process called abrasion. Abrasion is caused by sand, pebbles, etc rubbing against other rocks as they are carried by the running water (just like sandpaper wears away wood as it is rubbed against it). Over time the rocks along the bottom of the stream, or along the shoreline become rounded and smooth.
Running water can carry rock material in three ways;
1. Solution – this is material (mainly minerals) that is dissolved in the water. Iced tea, kool-aid, etc are examples of common solutions that we use (mixes dissolved in water).
2. Suspension – these are materials that heavier than water, but do not sink because the water is moving too quickly (small materials like fine sand, clay and silt). Materials carried in suspension usually make the water appear cloudy or muddy.
3. Bed Load – these are particles of sediment that are too heavy to be carried in suspension. They are pushed along the bottom (bed) of the stream/river.
The carrying power of a stream is the stream’s ability to transport particles. Carrying power depends on two things: 1.Speed – which is determined by the steepness or gradient of the land it is flowing over. The faster the stream moves, the larger the particles and the more particles it can carry (Reference Tables). 2.Discharge – is the volume of water flowing in the stream/river. The greater the discharge, the larger the particles and the more particles it can carry.
*As streams/rivers erode the land, they cut downward into the ground forming a V-shaped valley (ex. the Grand Canyon, AZ and the Ausable Chasm, NY).
The lowest level that a stream/river can erode downward is called the base level. If they flow into the ocean, base level is sea level. If they flow into a lake/river, then base level is the level of the lake /river.
*A river and all of its tributaries (smaller streams that flow into the larger one) are part of a river system. All of the land in which water drains into the river system is called a drainage basin or watershed. Drainage basins are usually very large (Mississippi River drainage basin), whereas watersheds are smaller areas (Croton watershed).
Stream Characteristics
Young streams tend to flow quickly and over a straight, narrow path. Over time the stream cuts deeper into the slope, and therefore the slope becomes less steep. Because of this, the stream slows down over time. It begins spread/cut outward instead of cutting downward.
As the stream widens, it begins to bend and wind back and forth (probably because it encounters rocks/obstructions that the slower moving stream can’t cut through, so it goes around them). This is called a meandering stream.
*As the water goes around the bend, the fastest water is on the outside of the turn (think about going down a water slide – around the turn you get pushed outward). This causes erosion to take place on the outside of the turn and the stream gets deeper here.
**The inside of the turn is where the water moves the slowest. This is where deposition takes place, and the stream becomes shallower.
Sometimes rivers may overflow its banks or flood. As the water spreads out to the sides of the river it slows down and deposits it sediment. This area is called a flood plain. These areas are some of the most fertile farmlands (because the soil is being recharged with nutrients when the sediment is deposited).
Deltas are formed at the mouths of rivers. Sediment is deposited as the river slows when it enters the larger body of water (Mississippi River Delta formed where the Mississippi River empties into the Gulf of Mexico). The delta has almost a triangular shape (like the Greek letter delta Δ).
Alluvial Fans are like deltas formed on dry land. Temporary streams formed by precipitation carry sediment down to the bottom of steep hills in dry areas. When the streams dry up, a large fan shaped pile of sediment is left behind.
Running Water
Stream Erosion and Transportation
Running water is all precipitation (rain, snow, etc) that falls on Earth that is pulled downhill by gravity. This running water originally gets its energy from the sun, since that is the source of energy for evaporation (which must occur for precipitation to form).
Running water breaks up the rocks by a mechanical weathering process called abrasion. Abrasion is caused by sand, pebbles, etc rubbing against other rocks as they are carried by the running water (just like sandpaper wears away wood as it is rubbed against it). Over time the rocks along the bottom of the stream, or along the shoreline become rounded and smooth.
Running water can carry rock material in three ways;
1. Solution – this is material (mainly minerals) that is dissolved in the water. Iced tea, kool-aid, etc are examples of common solutions that we use (mixes dissolved in water).
2. Suspension – these are materials that heavier than water, but do not sink because the water is moving too quickly (small materials like fine sand, clay and silt). Materials carried in suspension usually make the water appear cloudy or muddy.
3. Bed Load – these are particles of sediment that are too heavy to be carried in suspension. They are pushed along the bottom (bed) of the stream/river.
The carrying power of a stream is the stream’s ability to transport particles. Carrying power depends on two things:
1. Speed – which is determined by the steepness or gradient of the land it is flowing over. The faster the stream moves, the larger the particles and the more particles it can carry (Reference Tables).
2. Discharge – is the volume of water flowing in the stream/river. The greater the discharge, the larger the particles and the more particles it can carry.
*As streams/rivers erode the land, they cut downward into the ground forming a V-shaped valley (ex. the Grand Canyon, AZ and the Ausable Chasm, NY).
The lowest level that a stream/river can erode downward is called the base level. If they flow into the ocean, base level is sea level. If they flow into a lake/river, then base level is the level of the lake /river.
*A river and all of its tributaries (smaller streams that flow into the larger one) are part of a river system. All of the land in which water drains into the river system is called a drainage basin or watershed. Drainage basins are usually very large (Mississippi River drainage basin), whereas watersheds are smaller areas (Croton watershed).
Stream Characteristics
Young streams tend to flow quickly and over a straight, narrow path. Over time the stream cuts deeper into the slope, and therefore the slope becomes less steep. Because of this, the stream slows down over time. It begins spread/cut outward instead of cutting downward.As the stream widens, it begins to bend and wind back and forth (probably because it encounters rocks/obstructions that the slower moving stream can’t cut through, so it goes around them). This is called a meandering stream.
*As the water goes around the bend, the fastest water is on the outside of the turn (think about going down a water slide – around the turn you get pushed outward). This causes erosion to take place on the outside of the turn and the stream gets deeper here.
**The inside of the turn is where the water moves the slowest. This is where deposition takes place, and the stream becomes shallower.
Sometimes rivers may overflow its banks or flood. As the water spreads out to the sides of the river it slows down and deposits it sediment. This area is called a flood plain. These areas are some of the most fertile farmlands (because the soil is being recharged with nutrients when the sediment is deposited).
Deltas are formed at the mouths of rivers. Sediment is deposited as the river slows when it enters the larger body of water (Mississippi River Delta formed where the Mississippi River empties into the Gulf of Mexico). The delta has almost a triangular shape (like the Greek letter delta Δ).
Alluvial Fans are like deltas formed on dry land. Temporary streams formed by precipitation carry sediment down to the bottom of steep hills in dry areas. When the streams dry up, a large fan shaped pile of sediment is left behind.